Q: I was teaching my astronomy class about the ozone hole above Antarctica, and was asked if the scientists stationed there have to do anything special to protect themselves from the increased amount of UV light. I told them they must, but I really wasn't sure. Aren't the UV levels significantly higher there with the thinning of the ozone layer, and do the scientists stationed there take any special precautions? Thank you.

A: Those working in Antarctica, and also on Greenland's Ice Sheet in the summer have to worry about sunburn, but the ozone hole isn't the main reason.

Even before the ozone hole, sunburn and snow blindness were problems during the polar summer because ice reflects both visible light and ultraviolet energy. This more than makes up for the lower intensity of sunlight in the polar regions than in the tropics, where the sun is always nearly overhead at noon.

Here's something that makes you hurt when you think about it: While doing research for my latest book, The Complete Idiot's Guide to the Arctic and Antarctic, which was published in June 2003, I found accounts of early explorers getting the roofs of their mouths sunburned from sunlight reflected from the snow as they pulled sleds, with their mouths open, gasping for air.

When I went to Antarctica in January 1999, I was told to bring plenty of high-powered sunblock, and good sunglasses with UV protection. But, at this time, the UV index, a measure of the danger, at McMurdo on the coast was about what you'd find in San Diego, Calif., in April or September. At the South Pole, the index was lower than you'd find in San Diego on a sunny late December day.

Now, let's look at the effect of the Antarctic ozone hole. For more information on this, go to the USATODAY.com Understanding the Antarctic ozone hole page, where you will find links to a lot of information on what the hole is and how it works.

When you taught about the ozone hole, I'm sure you told your students how it forms each year when the sun begins coming up in Antarctica, reaches its peak in November and December, and begins filling in by late December or early January.

The links on the right of this page to "UV Indexes through the year," take you to plots of the UV indexes measured at San Diego, the Palmer Station in Antarctica, and the South Pole, beginning in 1997. They are on the Biospherical Instruments, Inc., website. This company operates the sensors in The National Science Foundation's Office of Polar Programs Ultraviolet (UV) Monitoring Network, which was established in 1987.

If you look at the plot of UV measurements for San Diego, you see that ultraviolet energy reaching the ground there is lowest around the beginning of the year, when days are the shortest and the sun is lowest in the sky. The amount of UV grows to the largest values in late June and early July when days are the longest, and the sun is highest in the sky.

Now, let's look at the plot for the South Pole Station. First, notice that it runs from July through June, not from January through December, like the San Diego plot. In other words, mid summer when the sun is highest in the sky is in the middle of the Antarctic graph.

The first thing that pops out from the South Pole plot is no UV until September and none after March, when the Pole is in six months of darkness. When the sun is up from late September, until March, you see the index went above a typical San Diego mid-winter day only in 1998, 1999, and 2001.

Look at the graph closely and you see the effect of the ozone hole. With normal, pretty much unchanging levels of ozone, the amount of UV would peak in late December when the sun is highest in the sky. We can't say days are longest because when the sun is up, daylight is 24 hours a day, every day at the Pole.

The late-November peak shows when the least amount of ozone is above the Pole. In some years the "hole" is thin enough to more than offset the fact that the sun isn't highest in the sky.

Something else that stands out, is that less UV reached the surface at the Pole from October through December 2002, which was the result of the ozone hole not being as deep, and breaking up sooner than in recent years. (Related stories: 2002 hole filled in early, and 2002 ozone hole smallest since 1988).

Finally, let's look at the plot for the Palmer Station on the Antarctic Peninsula. This is where the effects of the ozone hole show up the strongest, and where the effects are felt the most. As at the Pole, the highest UV levels are before the days when the sun is highest in the sky. And, they clearly show the year-to-year differences in the hole, with the UV index climbing higher than on a mid-summer day in San Diego a few times, even though the sun is much lower in the sky than during summer in San Diego.

In other words, those who work at the Palmer Station, where it's much warmer than at the Pole, do have to worry more about the added ultraviolet energy. But at worst, it would be about what you'd encounter in the tropics at noon.

People at the South Pole don't particularly worry about the added UV from the hole affecting them because they are so bundled up that almost no skin is exposed to sunburn. The temperature, which rarely goes above zero Fahrenheit even in the summer, is more of a danger to people than the UV. But, they do have to use sunblock on any exposed skin, such as the tips of their noses.

The Palmer Station, however, is on the shore of the Southern Ocean, which is where almost all of the living things that are likely to be effected by the ozone hole live.

As you can imagine, scientists are trying to learn the effects of the added ultraviolet radiation that the ozone hole allows to reach the ocean. In general, they've found some loss in the amount of phytoplankton (at the bottom of the food web), but no major problems.